1. Field of the Invention
The present invention relates to a lifting apparatus for use in assembling a building at an elevated spot, painting and the like at the elevated spot, lifting operators or materials upward for operation at the elevated spot or loading and unloading disused building materials at the building work, particularly to the lifting apparatus having a lifting mechanism for raising and lowering a platform which mechanism resembles hydraulic cylinders as a whole.
2. Prior Art
There has been employed a lifting apparatus provided with a platform for assembling, painting, repairing a building, and the like at an elevated spot, which platform is capable of lifting or lowering for loading operators or building materials and the like thereon or unloading the disused materials therefrom.
There has been employed a pantograph type telescopical mechanism, i.e. scissors type comprising a first pair of arms pivotally connected with each other at the central portion thereof and plural pairs of arms connected with the first pair of arms. In this apparatus, it was necessary to lengthen the length of the pairs of arms or increase the number of arms to be connected to the first pair of arms for increasing the height of the platform at maximum. Hence, if a lifting mechanism capable of lifting upward as high as possible is designed, it was necessary to employ a plurality of paired pantographs, which entails increasing the height of the lifting mechanism when folded and making it more troublesome for getting thereon or thereoff or loading the materials thereon or unloading the materials therefrom.
There have been various proposals to solve the problems set forth above, for example the one as disclosed in U.S. Pat. No. 3,820,631. In a mechanism as proposed by this patent, a lower boom and an upper boom are respectively capable of moving linearly into a middle boom and the lower boom is pivotally mounted on a chassis at the end thereof and the upper boom is pivotally mounted on a platform at the end thereof, and these booms are assembled to form an X-shape. In this mechanism, inasmuch as the length of the boom per se becomes long, the height of the platform when folded can be decreased and the platform can be raised at the elevated spot.
However, according to this invention, inasmuch as the mechanism for extending the lower boom and upper boom from the middle boom comprises a screw and a thread for engaging with this screw, the telescopic moving speed of the lower and upper booms relative to the middle boom is slow, hence the platform can not be moved quickly. Furthermore, since the sliding motion of the lower boom and the upper boom is made by a bevel gear provided at the central portion of the middle boom, the entire length of the combination of the lower boom and the upper boom extending from the middle boom reaches the length only half as long as the middle boom, hence the mechanism has such a structure that the platform can not be raised as high as possible.
There has been proposed such a mechanism that another boom is inserted into a boom to extend the length thereof so that the entire length thereof is lengthened.
For example, in FIG. 4 of Japanese Patent Laid-Open Publication No. 53-119556 lower and upper booms respectively having small diameters are inserted into a middle boom having a large diameter wherein the lower and upper booms inserted into the middle boom are pulled out to lengthen the entire length of the booms, whereby the platform is raised high.
However, according to this mechanism, there is no mechanism for synchronizing the amount of extension and contraction of the lower boom pulled out from the middle boom with that of the upper boom pulled out from the middle boom. The lower and the upper boom move individually relative to the middle boom. The amount of extension and contraction is restricted by a link mechanism comprising bars, hence the complete synchronization of the lower and upper boom relative to the middle boom can not be achieved. Accordingly, the lower and upper booms can not be connected to the platform by a pin and the like, and non-synchronized error of the amount of the extension and contraction between the lower and upper booms relative to the middle boom can be absorbed by rollers contacting the chassis and the platform. Hence, the platform is liable to swing because of accumulation of jolt caused by many supporting fulcrums and reception of the rolling motion by the roller. As a result, the mechanism is liable to swing by the wind and the like and is unstable, thereby permitting the operator to feel anxious.
In FIG. 4 of aforesaid No. 53-119556, the X-shaped middle boom can be turned by a hydraulic cylinder attached externally wherein the upper and lower booms are pulled out from the middle boom when the middle boom is turned. Although the amount of movement of the upper and lower booms from the middle boom when pulled out is restricted by a link mechanism, each length of the upper and lower booms when pulled out at maximum by the maximum extension of the hydraulic cylinder, which affects directly the upper and lower booms, does not exceed the entire length of the middle boom. Accordingly, it was impossible to extend the entire lengths of the booms at their maximum length.
There have been proposed many lifting mechanisms having a plurality of booms telescopically interfit into an arm which arm can be extended in the longitudinal direction thereof such as those as disclosed in Japanese Patent Application Nos. 56-134487 and 56-191065 (now Laid-Open Publication No. 58-95100). In these mechanisms, the booms composed of three stages are extendable in the longitudinal directions thereof and middle booms assembled in an X-shape can be turned at the central portions thereof wherein a chassis and a platform are structured to be the X-shape as viewed from the side view and the platform can be raised at the higher position. Furthermore, inasmuch as a lower boom and an upper boom are connected to the mobile chassis and the platform at the tip ends thereof by pins, there occurred less jolt, hence the structure can resist strong against the vibration. In the lifting mechanism having stretchable boom assemblies capable of stretching in several stages, the middle boom per se can be raised by a hydraulic cylinder intervened between the mobile chassis and the center of the middle boom and the lower boom or the upper boom are pulled out by the hydraulic cylinder inserted into the middle boom in order to telescopically move the lower boom or the upper boom from the middle boom. In this arrangement, inasmuch as the hydraulic cylinder can be used, it was necessary to synchronize the upper and lower boom relative to the middle boom, which entails necessity of a synchronous mechanism composed of chains or wires an the like. As a result, there was occurred such a problem that the arrangement was complex and the weight of the lifting mechanism was increased.